1. Field of the Invention
The invention relates to test probe positioning machines and, more particularly, to test probe positioning machines which can be controlled by a digital control system storing information representing test point locations of a printed circuit board to be tested.
More particularly, the invention relates to test probe positioning machines which avoid perpendicular V-way guides and the like for conveying a test probe assembly to a predetermined coordinate location.
2. Description of the Prior Art
Complex electronic systems are conventionally constructed from mass produced printed circuit boards whch must be reliably tested prior to use. Consequently, there is a great need for high speed, low cost, low maintenance, highly reliable systems and methods for automatically testing such printed circuit boards. Known digitally controlled printed circuit board test systems usually include computing devices which store information representative of the location of predetermined test points of a particular printed circuit board to be tested. The printed circuit board test systems also provide a predetermined sequence of input test signals designed to adequately exercise all of the electronic components of the printed circuit board being tested and also store information representing the known correct responses for preselected test points. The actually measured responses of the preselected test points are measured by contacting them with a test probe and comparing the response actually measured with the known correct responses, which can be stored in digital form or can be concurrently produced by applying the same input test pattern to a known good printed circuit board. Since the dimensions of test points on printed circuit boards are very small (in order to effect high density placement of electronic components on the printed circuit board), the automatic test probe apparatus must be capable of very precise movement of the test probe in order to move them into contact with a particular test point of a printed circuit board under test. One known digitally controllable automatic test probe system includes a pair of precisely positioned parallel, elongated machined elements having triangular cross-sections. The two triangular cross-sectioned members are mounted in the same plane and are referred to as "V-ways". A pair of slide blocks having triangular grooves in the bottom surface thereof slidably move along the V-ways (which are referred to as "X" V-ways), in a direction referred to as the "X" direction. The slide blocks support another pair of relatively closely spaced elongated V-ways which are perpendicular to the "X" V-ways and are referred to as the "Y" V-ways. A pair of spaced blocks having precision V-shaped grooves which mate with the respective "Y" V-ways move slidably in the Y direction and support a platform upon which a test probe is mounted. The test probe can be raised or lowered by mechanical connection to a solenoid activated by a control signal produced by the digital system. Movement of the "Y" V-ways in the "X" direction along the "X" V-ways is achieved by means of a first stepper motor which drives a long first threaded shaft. The first threaded shaft passes through a threaded nut block rigidly attached to the "Y" V-ways. The platform is moved in the "Y" direction along the "Y" V-ways by means of a second stepper motor which drives a second long shaft passing through a second nut block attached to the platform. Digital signals which activate the first and second stepper motors provide information representative of the X and Y coordinates of a particular test point of the printed circuit board to be tested. Programming of conventional computerized testing systems to provide the digital control signals for the first and second stepper motors and for activating the probe tip and for producing the necessary input test patterns to the printed circuit board under test are widely utilized in the electronics industry and are readily implemented by those skilled in the art. The above described system can attain the needed precision to automatically probe test points of state of the art printed circuit boards. However, the described system has numerous shortcomings, one being slowness of operation due to high mass and high inertia.
Accordingly, it is an object of the invention to provide a high precision, digitally controlled printed circuit board test system having high speed operation.
Another object of the invention is to provide a digitally controlled printed circuit board test system having sufficiently high precision to test present state of the art printed circuit boards and having low mass.
The above described digitally controlled test probe systems are extremely expensive because extremely high precision components are required to provide reliablility. The above described V-ways must be constructed with extremely precise tolerances in order that "binding" be avoided as the test probe is moved by means of the above described sliding action of the slide blocks along the machined V-way surface. Extremely precise alignment is required.
It is therefore still another object of the invention to provide a high precision digitally controllable test probe system which is relatively inexpensive.
A further object of the invention is to provide a high precision digitally controllable test probe system which avoids the need for precision alignment operations prior to use of the digitally controllable test probe system.
A yet further object of the invention is to provide a high precision digitally controllable test probe system which avoids the need for use of high precision V-ways and the like.
The described prior art test probe system has high maintenance costs due to the need for precision realignment due to wearing of the sliding surfaces. The sliding surfaces must be carefully lubricated. The lubricated surfaces have a tendency to accumulate dirt and grit, which increases wear and causes binding which impairs operation of the device.
It is therefore a still further object of the invention to provide a low cost, high precision digitally controlled test probe system which avoids the maintenance costs associated with the above described prior art system.
A novelty search directed to the present invention uncovered U.S. Pat. Nos. 3,184,740, 3,230,622, 3,438,133, 3,495,519, 3,561,125 and 3,564,533.